Myoepithelial cells are a dynamic barrier to epithelial dissemination

Targeting Tumor Heterogeneity by Breaking a Stem Cell and Epithelial Niche Interaction Loop

Tumor heterogeneity, the presence of multiple distinct subpopulations of cancer cells between patients or among the same tumors, poses a major challenge to current targeted therapies. The way these different subpopulations interact among themselves and the stromal niche environment, and how such interactions affect cancer stem cell behavior has remained largely unknown. Here, it is shown that an FGF-BMP7-INHBA signaling positive feedback loop integrates interactions among different cell populations, including mammary gland stem cells, luminal epithelial and stromal fibroblast niche components not only in organ regeneration but also, with certain modifications, in cancer progression. The reciprocal dependence of basal stem cells and luminal epithelium is based on basal-derived BMP7 and luminal-derived INHBA, which promote their respective expansion, and is regulated by stromal-epithelial FGF signaling. Targeting this interaction loop, for example, by reducing the function of one or more of its components, inhibits organ regeneration and breast cancer progression. The results have profound implications for overcoming drug resistance because of tumor heterogeneity in future targeted therapies.

Cyclical heat stress during lactation influences the microstructure of the bovine mammary gland

This study aimed to evaluate the impact of heat stress on mammary epithelial cell (MEC) losses into milk, secretory mammary tissue structure, and mammary epithelial cell activity. Sixteen multiparous Holstein cows (632 ± 12 kg BW) approximately 100 d in milk housed in climate-controlled rooms were paired by body weight and randomly allocated to one of 2 treatments, heat stress (HS) or pair feeding thermoneutral (PFTN) using 2 cohorts. Each cohort was subjected to 2 periods of 4 d each. In period 1, both treatments had ad libitum access to a common total mixed ration and were exposed to a controlled daily temperature-humidity index (THI) of 64. In period 2, HS cows were exposed to controlled cyclical heat stress (THI: 74 to 80), while PFTN cows remained at 64 THI and daily dry matter intake was matched to HS. Cows were milked twice daily, and milk yield was recorded at each milking. Individual milk samples on the last day of each period were used to quantify MEC losses by flow cytometry using butyrophilin as a cell surface marker. On the final day of period 2, individual bovine mammary tissue samples were obtained for histomorphology analysis, assessment of protein abundance, and evaluation of gene expression of targets associated with cellular capacity for milk and milk component synthesis, heat response, cellular proliferation, and autophagy. Statistical analysis was performed using the GLIMMIX procedure of SAS. Milk yield was reduced by 4.3 kg by HS (n = 7) compared with PFTN (n = 8). Independent of treatment, MEC in milk averaged 174 cells/mL (2.9% of total cells). There was no difference between HS vs. PFTN cows for MEC shed or concentration in milk. Alveolar area was reduced 25% by HS, and HS had 4.1 more alveoli than PFTN. Total number of nucleated MEC per area were greater in HS (389 ± 1.05) compared with PFTN (321 ± 1.05); however, cell number per alveolus was similar between groups (25 ± 1.5 vs. 26 ± 1.4). There were no differences in relative fold expression for GLUT1, GLUT8, CSN2, CSN3, LALBA, FASN, HSPA5, and HSPA8 in HS compared with PFTN. Immunoblotting analyses showed a decrease abundance for phosphorylated STAT5 and S6K1, and an increase in LC3 II in HS compared with PFTN. These results suggest that even if milk yield differences and histological changes occur in the bovine mammary gland after 4 d of heat exposure, MEC loss into milk, nucleated MEC number per alveolus, and gene expression of nutrient transport, milk component synthesis, and heat stress related targets are unaffected. In contrast, the abundance of proteins related to protein synthesis and cell survival decreased significantly, while an upregulation of proteins associated with autophagy in HS compared with PFTN.

A closer look into the cellular and molecular biology of myoepithelial cells across various exocrine glands

Myoepithelial cells (MECs) are a unique subset of epithelial cells that possess several smooth muscle cell characteristics, such as a high number of actin-myosin filaments and the ability to contract. These cells are primarily located around the secretory cells of exocrine glands, including the salivary, mammary, lacrimal, and sweat glands. Their primary functions involve the construction of the basement membrane and help with secretion of gland products through contraction. So far, no comparative analysis of MECs in different exocrine glands had ever evaluated their differences. In this review, we took advantage of the various publicly available scRNAseq data from mouse exocrine glands to identify their shared and unique characteristics. The aim of this review is to compare the role of MECs in maintaining healthy glandular function, their involvement in disease states, and their regenerative capacity, with a particular emphasis on the latest research findings in these areas.

Comprehensive single cell aging atlas of mammary tissues reveals shared epigenomic and transcriptomic signatures of aging and cancer

Aging is the greatest risk factor for breast cancer; however, how age-related cellular and molecular events impact cancer initiation is unknown. We investigate how aging rewires transcriptomic and epigenomic programs of mouse mammary glands at single cell resolution, yielding a comprehensive resource for aging and cancer biology. Aged epithelial cells exhibit epigenetic and transcriptional changes in metabolic, pro-inflammatory, or cancer-associated genes. Aged stromal cells downregulate fibroblast marker genes and upregulate markers of senescence and cancer-associated fibroblasts. Among immune cells, distinct T cell subsets (Gzmk+, memory CD4+, γδ) and M2-like macrophages expand with age. Spatial transcriptomics reveal co-localization of aged immune and epithelial cells in situ. Lastly, transcriptional signatures of aging mammary cells are found in human breast tumors, suggesting mechanistic links between aging and cancer. Together, these data uncover that epithelial, immune, and stromal cells shift in proportions and cell identity, potentially impacting cell plasticity, aged microenvironment, and neoplasia risk.

'Chip'-ing away at morphogenesis - application of organ-on-chip technologies to study tissue morphogenesis

Emergent cell behaviors that drive tissue morphogenesis are the integrated product of instructions from gene regulatory networks, mechanics and signals from the local tissue microenvironment. How these discrete inputs intersect to coordinate diverse morphogenic events is a critical area of interest. Organ-on-chip technology has revolutionized the ability to construct and manipulate miniaturized human tissues with organotypic three-dimensional architectures in vitro. Applications of organ-on-chip platforms have increasingly transitioned from proof-of-concept tissue engineering to discovery biology, furthering our understanding of molecular and mechanical mechanisms that operate across biological scales to orchestrate tissue morphogenesis. Here, we provide the biological framework to harness organ-on-chip systems to study tissue morphogenesis, and we highlight recent examples where organ-on-chips and associated microphysiological systems have enabled new mechanistic insight in diverse morphogenic settings. We further highlight the use of organ-on-chip platforms as emerging test beds for cell and developmental biology.

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

Inverse agonists of retinoic acid receptor/retinoid X receptor signaling as lineage-specific antitumor agents against human adenoid cystic carcinoma

BACKGROUND

Adenoid cystic carcinoma (ACC) is a lethal malignancy of exocrine glands, characterized by the coexistence within tumor tissues of 2 distinct populations of cancer cells, phenotypically similar to the myoepithelial and ductal lineages of normal salivary epithelia. The developmental relationship linking these 2 cell types, and their differential vulnerability to antitumor treatments, remains unknown.

METHODS

Using single-cell RNA sequencing, we identified cell-surface markers (CD49f, KIT) that enabled the differential purification of myoepithelial-like (CD49fhigh/KITneg) and ductal-like (CD49flow/KIT+) cells from patient-derived xenografts (PDXs) of human ACCs. Using prospective xenotransplantation experiments, we compared the tumor-initiating capacity of the 2 cell types and tested whether one could differentiate into the other. Finally, we searched for signaling pathways with differential activation between the 2 cell types and tested their role as lineage-specific therapeutic targets.

RESULTS

Myoepithelial-like cells displayed higher tumorigenicity than ductal-like cells and acted as their progenitors. Myoepithelial-like and ductal-like cells displayed differential expression of genes encoding for suppressors and activators of retinoic acid signaling, respectively. Agonists of retinoic acid receptor (RAR) or retinoid X receptor (RXR) signaling (all-trans retinoic acid, bexarotene) promoted myoepithelial-to-ductal differentiation, whereas suppression of RAR/RXR signaling with a dominant-negative RAR construct abrogated it. Inverse agonists of RAR/RXR signaling (BMS493, AGN193109) displayed selective toxicity against ductal-like cells and in vivo antitumor activity against PDX models of human ACC.

CONCLUSIONS

In human ACCs, myoepithelial-like cells act as progenitors of ductal-like cells, and myoepithelial-to-ductal differentiation is promoted by RAR/RXR signaling. Suppression of RAR/RXR signaling is lethal to ductal-like cells and represents a new therapeutic approach against human ACCs.

Configurational entropy is an intrinsic driver of tissue structural heterogeneity

Tissues comprise ordered arrangements of cells that can be surprisingly disordered in their details. How the properties of single cells and their microenvironment contribute to the balance between order and disorder at the tissue-scale remains poorly understood. Here, we address this question using the self-organization of human mammary organoids as a model. We find that organoids behave like a dynamic structural ensemble at the steady state. We apply a maximum entropy formalism to derive the ensemble distribution from three measurable parameters - the degeneracy of structural states, interfacial energy, and tissue activity (the energy associated with positional fluctuations). We link these parameters with the molecular and microenvironmental factors that control them to precisely engineer the ensemble across multiple conditions. Our analysis reveals that the entropy associated with structural degeneracy sets a theoretical limit to tissue order and provides new insight for tissue engineering, development, and our understanding of disease progression.

Pathology of breast cancer metastasis and a view of metastasis to the brain

Despite the advances in diagnosis and management of breast cancer, metastasis has been responsible for the staggering percentage of breast cancer-related death. Mortality threat can be explained mostly by the lack of proper understanding of the diversity of pathological features and underlying mechanism of breast cancer metastasis and effective targeted therapy. Breast cancer stem cells (BCSCs) are the potential source of tumor cells spread to distant organs. BCSCs targeted therapy can suppress the breast cancer progression to metastasis. Spreading of tumor cells to the bone, lung, liver, and brain occurs through a distinct non-random process; called metastasis organotropism. Recently, brain metastasis in breast cancer patients has been detected more frequently, causing a significant clinical burden. BRCA1 and BRCA2 associated breast cancers carry a remarkably higher propensity of CNS metastasis. BRCA1 and BRCA2 associated breast cancers commonly have the propensity to be the triple-negative (TN) and hormone receptors (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative molecular subtypes, respectively. Regardless of molecular subtypes, metastasis is most commonly evident at the bone. Heterogeneity is a critical pathological feature, leads to therapeutic resistance. BCSCs, biomarkers expression patterns, and mutations contribute to heterogeneity. In this paper, we discuss crucial pathological features of breast cancer metastasis, emphasizing metastasis organotropism and heterogeneity; and mechanisms of breast cancer metastasis, highlighting the pathways of metastasis to the brain. We consider that this paper reinforces future research areas and benefits the general readers, physicians, and researchers to identify potential areas to develop targeted therapies.

Organ Protection by Caloric Restriction Depends on Activation of the De Novo NAD+ Synthesis Pathway

SIGNIFICANCE STATEMENT

AKI is a major clinical complication leading to high mortality, but intensive research over the past decades has not led to targeted preventive or therapeutic measures. In rodent models, caloric restriction (CR) and transient hypoxia significantly prevent AKI and a recent comparative transcriptome analysis of murine kidneys identified kynureninase (KYNU) as a shared downstream target. The present work shows that KYNU strongly contributes to CR-mediated protection as a key player in the de novo nicotinamide adenine dinucleotide biosynthesis pathway. Importantly, the link between CR and NAD+ biosynthesis could be recapitulated in a human cohort.

BACKGROUND

Clinical practice lacks strategies to treat AKI. Interestingly, preconditioning by hypoxia and caloric restriction (CR) is highly protective in rodent AKI models. However, the underlying molecular mechanisms of this process are unknown.

METHODS

Kynureninase (KYNU) knockout mice were generated by Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and comparative transcriptome, proteome and metabolite analyses of murine kidneys pre- and post-ischemia-reperfusion injury in the context of CR or ad libitum diet were performed. In addition, acetyl-lysin enrichment and mass spectrometry were used to assess protein acetylation.

RESULTS

We identified KYNU as a downstream target of CR and show that KYNU strongly contributes to the protective effect of CR. The KYNU-dependent de novo nicotinamide adenine dinucleotide (NAD+) biosynthesis pathway is necessary for CR-associated maintenance of NAD+ levels. This finding is associated with reduced protein acetylation in CR-treated animals, specifically affecting enzymes in energy metabolism. Importantly, the effect of CR on de novo NAD+ biosynthesis pathway metabolites can be recapitulated in humans.

CONCLUSIONS

CR induces the de novo NAD+ synthesis pathway in the context of IRI and is essential for its full nephroprotective potential. Differential protein acetylation may be the molecular mechanism underlying the relationship of NAD+, CR, and nephroprotection.

Isogenic Mammary Models of Intraductal Carcinoma Reveal Progression to Invasiveness in the Absence of a Non-Obligatory In Situ Stage

In breast cancer, progression to invasive ductal carcinoma (IDC) involves interactions between immune, myoepithelial, and tumor cells. Development of IDC can proceed through ductal carcinoma in situ (DCIS), a non-obligate, non-invasive stage, or IDC can develop without evidence of DCIS and these cases associate with poorer prognosis. Tractable, immune-competent mouse models are needed to help delineate distinct mechanisms of local tumor cell invasion and prognostic implications. To address these gaps, we delivered murine mammary carcinoma cell lines directly into the main mammary lactiferous duct of immune-competent mice. Using two strains of immune-competent mice (BALB/c, C57BL/6), one immune-compromised (severe combined immunodeficiency; SCID) C57BL/6 strain, and six different murine mammary cancer cell lines (D2.OR, D2A1, 4T1, EMT6, EO771, Py230), we found early loss of ductal myoepithelial cell differentiation markers p63, α-smooth muscle actin, and calponin, and rapid formation of IDC in the absence of DCIS. Rapid IDC formation also occurred in the absence of adaptive immunity. Combined, these studies demonstrate that loss of myoepithelial barrier function does not require an intact immune system, and suggest that these isogenic murine models may prove a useful tool to study IDC in the absence of a non-obligatory DCIS stage-an under-investigated subset of poor prognostic human breast cancer.

Everybody needs good neighbours: the progressive DCIS microenvironment

Ductal carcinoma in situ (DCIS) is a pre-invasive form of breast cancer where neoplastic luminal cells are confined to the ductal tree. While as many as 70% of DCIS cases will remain indolent, most women are treated with surgery, often combined with endocrine and radiotherapies. Overtreatment is therefore a major issue, demanding new methods to stratify patients. Somewhat paradoxically, the neoplastic cells in DCIS are genetically comparable to those in invasive disease, suggesting the tumour microenvironment is the driving force for progression. Clinical and mechanistic studies highlight the complex DCIS microenvironment, with multiple cell types competing to regulate progression. Here, we examine recent studies detailing distinct aspects of the DCIS microenvironment and discuss how these may inform more effective care.

Fibroblasts as Turned Agents in Cancer Progression

Differentiated epithelial cells reside in the homeostatic microenvironment of the native organ stroma. The stroma supports their normal function, their G0 differentiated state, and their expansion/contraction through the various stages of the life cycle and physiologic functions of the host. When malignant transformation begins, the microenvironment tries to suppress and eliminate the transformed cells, while cancer cells, in turn, try to resist these suppressive efforts. The tumor microenvironment encompasses a large variety of cell types recruited by the tumor to perform different functions, among which fibroblasts are the most abundant. The dynamics of the mutual relationship change as the sides undertake an epic battle for control of the other. In the process, the cancer “wounds” the microenvironment through a variety of mechanisms and attracts distant mesenchymal stem cells to change their function from one attempting to suppress the cancer, to one that supports its growth, survival, and metastasis. Analogous reciprocal interactions occur as well between disseminated cancer cells and the metastatic microenvironment, where the microenvironment attempts to eliminate cancer cells or suppress their proliferation. However, the altered microenvironmental cells acquire novel characteristics that support malignant progression. Investigations have attempted to use these traits as targets of novel therapeutic approaches.

Polarity in breast development and cancer

Mammary gland development and breast cancer progression are associated with extensive remodeling of epithelial tissue architecture. Apical-basal polarity is a key feature of epithelial cells that coordinates key elements of epithelial morphogenesis including cell organization, proliferation, survival, and migration. In this review we discuss advances in our understanding of how apical-basal polarity programs are used in breast development and cancer. We describe cell lines, organoids, and in vivo models commonly used for studying apical-basal polarity in breast development and disease and discuss advantages and limitations of each. We also provide examples of how core polarity proteins regulate branching morphogenesis and lactation during development. We describe alterations to core polarity genes in breast cancer and their associations with patient outcomes. The impact of up- or down-regulation of key polarity proteins in breast cancer initiation, growth, invasion, metastasis, and therapeutic resistance are discussed. We also introduce studies demonstrating that polarity programs are involved in regulating the stroma, either through epithelial-stroma crosstalk, or through signaling of polarity proteins in non-epithelial cell types. Overall, a key concept is that the function of individual polarity proteins is highly contextual, depending on developmental or cancer stage and cancer subtype.

Breast lesions with myoepithelial phenotype

Myoepithelial cells (MECs) constitute a continuous layer of cells surrounding the breast glands, localised between the epithelial cells (ECs) and the basal membrane. MECs play important roles in normal mammary gland as they produce basal membrane and stimulate secretion. During neoplastic transformation, MECs act as a barrier preventing stromal invasion. MECs themselves can undergo a great variety of changes, ranging from hyperplastic to metaplastic, to neoplastic, and giving rise to a wide spectrum of morphological pictures sometimes difficult to interpret on routine diagnoses. Several benign and malignant breast tumours can present features of MECs differentiation. As these latter tumours are quite infrequent, the purpose of the present study is to offer a review of the morphological spectrum of MECs lesions, with correlations to prognosis.

Identifying recurrences and metastasis after ductal carcinoma in situ (DCIS) of the breast

Ductal carcinoma in situ (DCIS) of the breast is a non-invasive tumour that has the potential to progress to invasive ductal carcinoma (IDC). Thus, it represents a treatment dilemma: alone it does not present a risk to life, however, left untreated it may progress to a life-threatening condition. Current clinico-pathological features cannot accurately predict which patients with DCIS have invasive potential, and therefore clinicians are unable to quantify the risk of progression for an individual patient. This leads to many women being over-treated, while others may not receive sufficient treatment to prevent invasive recurrence. A better understanding of the molecular features of DCIS, both tumour-intrinsic and the microenvironment, could offer the ability to better predict which women need aggressive treatment, and which can avoid therapies carrying significant side-effects and such as radiotherapy. In this review, we summarise the current knowledge of DCIS, and consider future research directions.

Re-evaluation of the myoepithelial cells roles in the breast cancer progression

Over the past decades, luminal epithelial cell lineage has gained considerable attraction as the functionally milk-secreting units and as the most fruitful acreage for breast cancer launching. Recognition of the effective involvement of the myoepithelial cells in mammary gland development and in hampering tumorigenesis has renewed the interest in investigating the biological roles of this second main mammary lineage. The human breast is made up of an extensively branching ductal system intervening by copious lobular units. The ductal system is coated by a chain of luminal epithelial cells (LECs) situated on a layer of myoepithelial cells (MECs) and encompassed by a distinguished basement membrane. Ductal contractility during lactation is a well-known function delivered by the MECs however this is not the only assignment mediated by these cellular populations. It has been well appreciated that the MECs exhibit a natural paracrine power in defeating cancer development and advancement. MECs were found to express numerous proteinase inhibitors, anti-angiogenic factors, and tumour suppressors proteins. Additionally, MECs contributed effectively to maintaining the right luminal cells' polarization and further separating them from the adjacent stroma by making an integrated fence. Indeed, disruption of the MECs layer was reported to facilitate the invasion of the cancer cells to the surrounding stroma. Nonetheless, MECs were also found to exhibit cancer-promoting effects and provoke tumour invasion and dissemination by displaying distinct cancer chemokines. Herein in this review, we aimed to address the roles delivered by MECs in breast cancer progression and decipher the molecular mechanisms regulating proper MECs' physiology, integrity, and terminal differentiation.

Clinical applications of 3D normal and breast cancer organoids: A review of concepts and methods

While mouse models and two-dimensional (2D) cell culture systems have dominated as research tools for cancer biology, three-dimensional (3D) cultures have gained traction as a new approach that retains features of in vivo biology within an in vitro system. Over time, 3D culture systems have evolved from spheroids and tumorspheres to organoids, and by doing so, they have become more complex and representative of original tissue. Such technological improvements have mostly benefited the study of heterogeneous solid tumors, like those found in breast cancer (BC), by providing an attractive avenue for scalable drug testing and biobank generation. Experimentally, organoids have been used in the BC field to dissect mechanisms related to cellular invasion and metastasis-and through co-culture methods-epithelial interactions with stromal and immune cells. In addition, organoid studies of wild-type mouse models and healthy donor samples have provided insight into the basic developmental cellular and molecular biology of the mammary gland, which may inform one's understanding of the initial stages of cancer development and progression.

Mechanostimulation of breast myoepithelial cells induces functional changes associated with DCIS progression to invasion

Women with ductal carcinoma in situ (DCIS) have an increased risk of progression to invasive breast cancer. Although not all women with DCIS will progress to invasion, all are treated as such, emphasising the need to identify prognostic biomarkers. We have previously shown that altered myoepithelial cells in DCIS predict disease progression and recurrence. By analysing DCIS duct size in sections of human breast tumour samples, we identified an associated upregulation of integrin β6 and an increase in periductal fibronectin deposition with increased DCIS duct size that associated with the progression of DCIS to invasion. Our modelling of the mechanical stretching myoepithelial cells undergo during DCIS progression confirmed the upregulation of integrin β6 and fibronectin expression in isolated primary and cell line models of normal myoepithelial cells. Our studies reveal that this mechanostimulated DCIS myoepithelial cell phenotype enhances invasion in a TGFβ-mediated upregulation of MMP13. Immunohistochemical analysis identified that MMP13 was specifically upregulated in DCIS, and it was associated with progression to invasion. These findings implicate tissue mechanics in altering the myoepithelial cell phenotype in DCIS, and that these alterations may be used to stratify DCIS patients into low and high risk for invasive progression.

Mechanisms of Basement Membrane Micro-Perforation during Cancer Cell Invasion into a 3D Collagen Gel

Cancer invasion through basement membranes represents the initial step of tumor dissemination and metastasis. However, little is known about how human cancer cells breach basement membranes. Here, we used a three-dimensional in vitro invasion model consisting of cancer spheroids encapsulated by a basement membrane and embedded in 3D collagen gels to visualize the early events of cancer invasion by confocal microscopy and live-cell imaging. Human breast cancer cells generated large numbers of basement membrane perforations, or holes, of varying sizes that expanded over time during cell invasion. We used a wide variety of small molecule inhibitors to probe the mechanisms of basement membrane perforation and hole expansion. Protease inhibitor treatment (BB94), led to a 63% decrease in perforation size. After myosin II inhibition (blebbistatin), the basement membrane perforation area decreased by only 15%. These treatments produced correspondingly decreased cellular breaching events. Interestingly, inhibition of actin polymerization dramatically decreased basement membrane perforation by 80% and blocked invasion. Our findings suggest that human cancer cells can primarily use proteolysis and actin polymerization to perforate the BM and to expand perforations for basement membrane breaching with a relatively small contribution from myosin II contractility.

Mapping hormone-regulated cell-cell interaction networks in the human breast at single-cell resolution

The rise and fall of estrogen and progesterone across menstrual cycles and during pregnancy regulates breast development and modifies cancer risk. How these hormones impact each cell type in the breast remains poorly understood because they act indirectly through paracrine networks. Using single-cell analysis of premenopausal breast tissue, we reveal a network of coordinated transcriptional programs representing the tissue-level response to changing hormone levels. Our computational approach, DECIPHER-seq, leverages person-to-person variability in breast composition and cell state to uncover programs that co-vary across individuals. We use differences in cell-type proportions to infer a subset of programs that arise from direct cell-cell interactions regulated by hormones. Further, we demonstrate that prior pregnancy and obesity modify hormone responsiveness through distinct mechanisms: obesity reduces the proportion of hormone-responsive cells, whereas pregnancy dampens the direct response of these cells to hormones. Together, these results provide a comprehensive map of the cycling human breast.

Tissue architecture in tumor initiation and progression

The 3D architecture of tissues bearing tumors impacts on the mechanical microenvironment of cancer, the accessibility of stromal cells, and the routes of invasion. A myriad of intrinsic and extrinsic forces exerted by the cancer cells, the host tissue, and the molecular and cellular microenvironment modulate the morphology of the tumor and its malignant potential through mechanical, biochemical, genetic, and epigenetic cues. Recent studies have investigated how tissue architecture influences cancer biology from tumor initiation and progression to distant metastatic seeding and response to therapy. With a focus on carcinoma, the most common type of cancer, this review discusses the latest discoveries on how tumor architecture is built and how tissue morphology affects the biology and progression of cancer cells.

Regulation of Tumor Invasion by the Physical Microenvironment: Lessons from Breast and Brain Cancer

The success of anticancer therapies is often limited by heterogeneity within and between tumors. While much attention has been devoted to understanding the intrinsic molecular diversity of tumor cells, the surrounding tissue microenvironment is also highly complex and coevolves with tumor cells to drive clinical outcomes. Here, we propose that diverse types of solid tumors share common physical motifs that change in time and space, serving as universal regulators of malignancy. We use breast cancer and glioblastoma as instructive examples and highlight how invasion in both diseases is driven by the appropriation of structural guidance cues, contact-dependent heterotypic interactions with stromal cells, and elevated interstitial fluid pressure and flow. We discuss how engineering strategies show increasing value for measuring and modeling these physical properties for mechanistic studies. Moreover, engineered systems offer great promise for developing and testing novel therapies that improve patient prognosis by normalizing the physical tumor microenvironment. Expected final online publication date for the Annual Review of Biomedical Engineering, Volume 24 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Transition to invasive breast cancer is associated with progressive changes in the structure and composition of tumor stroma

Ductal carcinoma in situ (DCIS) is a pre-invasive lesion that is thought to be a precursor to invasive breast cancer (IBC). To understand the changes in the tumor microenvironment (TME) accompanying transition to IBC, we used multiplexed ion beam imaging by time of flight (MIBI-TOF) and a 37-plex antibody staining panel to interrogate 79 clinically annotated surgical resections using machine learning tools for cell segmentation, pixel-based clustering, and object morphometrics. Comparison of normal breast with patient-matched DCIS and IBC revealed coordinated transitions between four TME states that were delineated based on the location and function of myoepithelium, fibroblasts, and immune cells. Surprisingly, myoepithelial disruption was more advanced in DCIS patients that did not develop IBC, suggesting this process could be protective against recurrence. Taken together, this HTAN Breast PreCancer Atlas study offers insight into drivers of IBC relapse and emphasizes the importance of the TME in regulating these processes.

Cell-extracellular matrix dynamics

The sites of interaction between a cell and its surrounding microenvironment serve as dynamic signaling hubs that regulate cellular adaptations during developmental processes, immune functions, wound healing, cell migration, cancer invasion and metastasis, as well as in many other disease states. For most cell types, these interactions are established by integrin receptors binding directly to extracellular matrix proteins, such as the numerous collagens or fibronectin. For the cell, these points of contact provide vital cues by sampling environmental conditions, both chemical and physical. The overall regulation of this dynamic interaction involves both extracellular and intracellular components and can be highly variable. In this review, we highlight recent advances and hypotheses about the mechanisms and regulation of cell-ECM interactions, from the molecular to the tissue level, with a particular focus on cell migration. We then explore how cancer cell invasion and metastasis are deeply rooted in altered regulation of this vital interaction.

Single Organoids Droplet-Based Staining Method for High-End 3D Imaging of Mammary Organoids

In the last decade, organoids became a tremendously popular technique in developmental and cancer biology for their high pathophysiological relevance to in vivo models with the advantage of easier manipulation, real-time observation, potential for high-throughput studies, and reduced ethical issues. Among other fundamental biological questions, mammary organoids have helped to reveal mechanisms of mammary epithelial morphogenesis, mammary stem cell potential, regulation of lineage specification, mechanisms of breast cancer invasion or resistance to therapy, and their regulation by stromal microenvironment. To exploit the potential of organoid technology to the fullest, together with optimal organoid culture protocols, visualization of organoid architecture and composition in high resolution in three dimensions (3D) is required. Whole-mount imaging of immunolabeled organoids enables preservation of the 3D cellular context, but conventional confocal microscopy of organoid cultures struggles with the large organoid sample size and relatively long distance from the objective to the organoid due to the 3D extracellular matrix (ECM) that surrounds the organoid. We have overcome these issues by physical separation of single organoids with their immediate stroma from the bulk ECM. Here we provide a detail protocol for the procedure, which entails single organoid collection and droplet-based staining and clearing to allow visualization of organoids in the greatest detail.

Deletion of Col15a1 Modulates the Tumour Extracellular Matrix and Leads to Increased Tumour Growth in the MMTV-PyMT Mouse Mammary Carcinoma Model

Basement membrane (BM) zone-associated collagen XV (ColXV) has been shown to suppress the malignancy of tumour cells, and its restin domain can inhibit angiogenesis. In human breast cancer, as well as in many other human carcinomas, ColXV is lost from the epithelial BM zone prior to tumour invasion. Here, we addressed the roles of ColXV in breast carcinogenesis using the transgenic MMTV-PyMT mouse mammary carcinoma model. We show here for the first time that the inactivation of Col15a1 in mice leads to changes in the fibrillar tumour matrix and to increased mammary tumour growth. ColXV is expressed by myoepithelial and endothelial cells in mammary tumours and is lost from the ductal BM along with the loss of the myoepithelial layer during cancer progression while persisting in blood vessels and capillaries, even in invasive tumours. However, despite the absence of anti-angiogenic restin domain, neovascularisation was reduced rather than increased in the ColXV-deficient mammary tumours compared to controls. We also show that, in robust tumour cell transplantation models or in a chemical-induced fibrosarcoma model, the inactivation of Col15a1 does not affect tumour growth or angiogenesis. In conclusion, our results support the proposed tumour suppressor function of ColXV in mammary carcinogenesis and reveal diverse roles of this collagen in different cancer types.

Evidence for accelerated aging in mammary epithelia of women carrying germline BRCA1 or BRCA2 mutations

During aging in the human mammary gland, luminal epithelial cells lose lineage fidelity by expressing markers normally expressed in myoepithelial cells. We hypothesize that loss of lineage fidelity is a general manifestation of epithelia that are susceptible to cancer initiation. In the present study, we show that histologically normal breast tissue from younger women who are susceptible to breast cancer, as a result of harboring a germline mutation in BRCA1, BRCA2 or PALB2 genes, exhibits hallmarks of accelerated aging. These include proportionately increased luminal epithelial cells that acquired myoepithelial markers, decreased proportions of myoepithelial cells and a basal differentiation bias or failure of differentiation of cKit+ progenitors. High-risk luminal and myoepithelial cells are transcriptionally enriched for genes of the opposite lineage, inflammatory- and cancer-related pathways. We have identified breast-aging hallmarks that reflect a convergent biology of cancer susceptibility, regardless of the specific underlying genetic or age-dependent risk or the associated breast cancer subtype.

Generation of ductal organoids from normal mammary luminal cells reveals invasive potential

Here we present an experimental model for human luminal progenitor cells that enables single, primary cells isolated from normal tissue to generate complex branched structures resembling the ductal morphology of low-grade carcinoma of no special type. Thereby, we find that ductal structures are generated through invasive branching morphogenesis via matrix remodeling and identify reduced actomyosin contractility as a prerequisite for invasion. In addition, we show that knockout of E-cadherin causes a dissolution of duct formation as observed in invasive lobular carcinoma, a subtype of invasive carcinomas where E-cadherin function is frequently lost. Thus, our model shows that invasive capacity can be elicited from normal luminal cells in specific environments, which results in low-grade no special type morphology. This assay offers a platform to investigate the dynamics of luminal cell invasion and unravel the impact of genetic and non-genetic aberrations on invasive morphology. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Tumour microenvironment 3D-modelling: simplicity to complexity and back again

Tumours are surrounded by a host of noncancerous cells that fulfil both supportive and suppressive roles within the tumour microenvironment (TME). The drive to understand the biology behind each of these components has led to a rapid expansion in the number and use of 3D in vitro models, as researchers find ways to incorporate multiple cell types into physiomimetic configurations. The use and increasing complexity of these models does however demand many considerations. In this review we discuss approaches adopted to recapitulate complex tumour biology in tractable 3D models. We consider how these cell types can be sourced and combined and examine methods for the deconvolution of complex multicellular models into manageable and informative outputs.

Organoids in cancer research: a review for pathologist-scientists

The use of three-dimensional (3D) culture models for cancer research has expanded greatly in recent years, with studies in almost every tumor type addressing a wide variety of research questions. Multiple distinct 3D culture approaches are now available, each with its own advantages and disadvantages, as well as most effective applications. In this review, we focus on one of these 3D culture models, organoids, in which multicellular units are isolated from primary or metastatic tumors and cultured in extracellular matrix gels. Organoids can be studied in acute cultures for short times after isolation, or passaged and biobanked for long-term use. We define this model system and describe some key studies in which organoid culture models were used to investigate cellular strategies and molecular mechanisms driving cancer initiation and progression, highlighting research questions for which this model is particularly well suited. In addition, as interest in implementing organoid systems continues to expand, we discuss key considerations in developing a new organoid research program. Our goal is to demonstrate the power and utility of organoid models and provide guidance for investigators who are considering implementation of these models in their own research programs. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cytokeratin 5 determines maturation of the mammary myoepithelium

At invasion, transformed mammary epithelial cells expand into the stroma through a disrupted myoepithelial (ME) cell layer and basement membrane (BM). The intact ME cell layer has thus been suggested to act as a barrier against invasion. Here, we investigate the mechanisms behind the disruption of ME cell layer. We show that the expression of basal/ME proteins CK5, CK14, and α-SMA altered along increasing grade of malignancy, and their loss affected the maintenance of organotypic 3D mammary architecture. Furthermore, our data suggests that loss of CK5 prior to invasive stage causes decreased levels of Zinc finger protein SNAI2 (SLUG), a key regulator of the mammary epithelial cell lineage determination. Consequently, a differentiation bias toward luminal epithelial cell type was detected with loss of mature, α-SMA-expressing ME cells and reduced deposition of basement membrane protein laminin-5. Therefore, our data discloses the central role of CK5 in mammary epithelial differentiation and maintenance of normal ME layer.

Neural EGFL like 2 expressed in myoepithelial cells and suppressed breast cancer cell migration

Breast tissue has a branching structure that contains double-layered cells, consisting primarily of luminal epithelial cells inside and myoepithelial cells outside. Ductal carcinoma in situ (DCIS) still has myoepithelial cells surrounding the cancer cells. However, myoepithelial cells disappear in invasive ductal carcinoma. In this study, we detected expression of neural EGFL like (NELL) 2 and one of its receptors, roundabout guidance receptor (ROBO) 3, in myoepithelial and luminal epithelial cells (respectively) in normal breast tissue. NELL2 also was expressed in myoepithelial cells surrounding the non-cancerous intraductal proliferative lesions and DCIS. However, the expression level and proportion of NELL2-positive cells in DCIS were lower than those in normal and non-cancerous intraductal proliferative lesions. ROBO3 expression was decreased in invasive ductal carcinoma compared to that in normal and non-cancerous intraductal proliferative lesions. An evaluation of NELL2's function in breast cancer cell lines demonstrated that full-length NELL2 suppressed cell adhesion and migration in vitro. In contrast, the N-terminal domain of NELL2 increased cell adhesion in the early phase and migration in vitro in some breast cancer cells. These results suggested that full-length NELL2 protein, when expressed in myoepithelial cells, might serve as an inhibitor of breast cancer cell migration.

KYNU, a novel potential target that underpins CD44-promoted breast tumour cell invasion

Using a validated tetracycline‐off‐inducible CD44 expression system in mouse model, we have previously demonstrated that the hyaluronan (HA) receptor CD44 promotes breast cancer (BC) metastasis to the liver. To unravel the mechanisms that underpin CD44‐promoted BC cell invasion, RNA samples were isolated from two cell models: (a) a tetracycline (Tet)‐Off‐regulated expression system of the CD44s in MCF‐7 cells and; (b) as a complementary approach, the highly metastatic BC cells, MDA‐MB‐231, were cultured in the presence and absence of 50 µg/mL of HA. Kynureninase (KYNU), identified by Microarray analysis, was up‐regulated by 3‐fold upon induction and activation of CD44 by HA; this finding suggests that KYNU is a potential novel transcriptional target of CD44‐downtstream signalling. KYNU is a pyridoxal phosphate (PLP) dependent enzyme involved in the biosynthesis of NAD cofactors from tryptophan that has been associated with the onset and development of BC. This review will attempt to identify and discuss the findings supporting this hypothesis and the mechanisms linking KYNU cell invasion via CD44.

The Adipose Microenvironment Dysregulates the Mammary Myoepithelial Cells and Could Participate to the Progression of Breast Cancer

Breast cancer is the most common cancer among women worldwide. Overweight and obesity are now recognized as established risk factors for this pathology in postmenopausal women. These conditions are also believed to be responsible for higher recurrence and mortality rates. Reciprocal interactions have been described between adipose and cancer cells. An adipose microenvironment favors a greater proliferation of cancer cells, their invasion and even resistance to anti-cancer treatments. In addition, the chronic low-grade inflammation observed in obese individuals is believed to amplify these processes. Among the cell types present in the breast, myoepithelial cells (MECs), located at the interface of the epithelial cells and the stroma, are considered "tumor suppressor" cells. During the transition from ductal carcinoma in situ to invasive cancer, disorganization or even the disappearance of MECs is observed, thereby enhancing the ability of the cancer cells to migrate. As the adipose microenvironment is now considered as a central actor in the progression of breast cancer, our objective was to evaluate if it could be involved in MEC functional modifications, leading to the transition of in situ to invasive carcinoma, particularly in obese patients. Through a co-culture model, we investigated the impact of human adipose stem cells from women of normal weight and obese women, differentiated or not into mature adipocytes, on the functionality of the MECs by measuring changes in viability, apoptosis, gene, and miRNA expressions. We found that adipose cells (precursors and differentiated adipocytes) could decrease the viability of the MECs, regardless of the original BMI. The adipose cells could also disrupt the expression of the genes involved in the maintenance of the extracellular matrix and to amplify the expression of leptin and inflammatory markers. miR-122-5p and miR-132-3p could also be considered as targets for adipose cells. The metabolite analyses revealed specific profiles that may be involved in the growth of neoplastic cells. All of these perturbations could thus be responsible for the loss of tumor suppressor status of MECs and promote the transition from in situ to invasive carcinoma.

Mammary Organoids and 3D Cell Cultures: Old Dogs with New Tricks

3D cell culture methods have been an integral part of and an essential tool for mammary gland and breast cancer research for half a century. In fact, mammary gland researchers, who discovered and deciphered the instructive role of extracellular matrix (ECM) in mammary epithelial cell functional differentiation and morphogenesis, were the pioneers of the 3D cell culture techniques, including organoid cultures. The last decade has brought a tremendous increase in the 3D cell culture techniques, including modifications and innovations of the existing techniques, novel biomaterials and matrices, new technological approaches, and increase in 3D culture complexity, accompanied by several redefinitions of the terms "3D cell culture" and "organoid". In this review, we provide an overview of the 3D cell culture and organoid techniques used in mammary gland biology and breast cancer research. We discuss their advantages, shortcomings and current challenges, highlight the recent progress in reconstructing the complex mammary gland microenvironment in vitro and ex vivo, and identify the missing 3D cell cultures, urgently needed to aid our understanding of mammary gland development, function, physiology, and disease, including breast cancer.

Aging-Associated Alterations in Mammary Epithelia and Stroma Revealed by Single-Cell RNA Sequencing

Aging is closely associated with increased susceptibility to breast cancer, yet there have been limited systematic studies of aging-induced alterations in the mammary gland. Here, we leverage high-throughput single-cell RNA sequencing to generate a detailed transcriptomic atlas of young and aged murine mammary tissues. By analyzing epithelial, stromal, and immune cells, we identify age-dependent alterations in cell proportions and gene expression, providing evidence that suggests alveolar maturation and physiological decline. The analysis also uncovers potential pro-tumorigenic mechanisms coupled to the age-associated loss of tumor suppressor function and change in microenvironment. In addition, we identify a rare, age-dependent luminal population co-expressing hormone-sensing and secretory-alveolar lineage markers, as well as two macrophage populations expressing distinct gene signatures, underscoring the complex heterogeneity of the mammary epithelia and stroma. Collectively, this rich single-cell atlas reveals the effects of aging on mammary physiology and can serve as a useful resource for understanding aging-associated cancer risk.

Using single-cell RNA-sequencing, Li et al. compare mammary epithelia and stroma in young and aged mice. Age-dependent changes at cell and gene levels provide evidence suggesting alveolar maturation, functional deterioration, and potential pro-tumorigenic and inflammatory alterations. Additionally, identification of heterogeneous luminal and macrophage subpopulations underscores the complexity of mammary lineages.

Interleukin-6-mediated epigenetic control of the VEGFR2 gene induces disorganized angiogenesis in human breast tumors

Disorganized vessels in the tumor vasculature lead to impaired perfusion, resulting in reduced accessibility to immune cells and chemotherapeutic drugs. In the breast tumor-stroma interplay, paracrine factors such as interleukin-6 (IL-6) often facilitate disordered angiogenesis. We show here that epigenetic mechanisms regulate the crosstalk between IL-6 and vascular endothelial growth factor receptor 2 (VEGFR2) signaling pathways in myoepithelial (CD10+) and endothelial (CD31+, CD105+, CD146+, and CD133-) cells isolated from malignant and nonmalignant tissues of clinically characterized human breast tumors. Tumor endothelial (Endo-T) cells in 3D cultures exhibited higher VEGFR2 expression levels, accelerated migration, invasion, and disorganized sprout formation in response to elevated IL-6 levels secreted by tumor myoepithelial (Epi-T) cells. Constitutively, compared with normal endothelial (Endo-N) cells, Endo-T cells differentially expressed DNA methyltransferase isoforms and had increased levels of IL-6 signaling intermediates such as IL-6R and signal transducer and activator of transcription 3 (STAT3). Upon IL-6 treatment, Endo-N and Endo-T cells displayed altered expression of the DNA methyltransferase 1 (DNMT1) isoform. Mechanistic studies revealed that IL-6 induced proteasomal degradation of DNMT1, but not of DNMT3A and DNMT3B and subsequently led to promoter hypomethylation and expression/activation of VEGFR2. IL-6-induced VEGFR2 up-regulation was inhibited by overexpression of DNMT1. Transfection of a dominant-negative STAT3 mutant, but not of STAT1, abrogated VEGFR2 expression. Our results indicate that in the breast tumor microenvironment, IL-6 secreted from myoepithelial cells influences DNMT1 stability, induces the expression of VEGFR2 in endothelial cells via a promoter methylation-dependent mechanism, and leads to disordered angiogenesis.

Organotypic culture assays for murine and human primary and metastatic-site tumors

Cancer invasion and metastasis are challenging to study in vivo since they occur deep inside the body over extended time periods. Organotypic 3D culture of fresh tumor tissue enables convenient real-time imaging, genetic and microenvironmental manipulation and molecular analysis. Here, we provide detailed protocols to isolate and culture heterogenous organoids from murine and human primary and metastatic site tumors. The time required to isolate organoids can vary based on the tissue and organ type but typically takes <7 h. We describe a suite of assays that model specific aspects of metastasis, including proliferation, survival, invasion, dissemination and colony formation. We also specify comprehensive protocols for downstream applications of organotypic cultures that will allow users to (i) test the role of specific genes in regulating various cellular processes, (ii) distinguish the contributions of several microenvironmental factors and (iii) test the effects of novel therapeutics.

Organoids as Complex In Vitro Models for Studying Radiation-Induced Cell Recruitment

Patients with triple negative breast cancer (TNBC) typically receive chemotherapy, surgery, and radiation therapy. Although this treatment improves prognosis for most patients, some patients continue to experience recurrence within 5 years. Preclinical studies have shown that immune cell infiltration at the irradiated site may play a significant role in tumor cell recruitment; however, little is known about the mechanisms that govern this process. This lack of knowledge highlights the need to evaluate radiation-induced cell infiltration with models that have controllable variables and maintain biological integrity. Mammary organoids are multicellular three-dimensional (3D) in vitro models, and they have been used to examine many aspects of mammary development and tumorigenesis. Organoids are also emerging as a powerful tool to investigate normal tissue radiation damage. In this review, we evaluate recent advances in mammary organoid technology, consider the advantages of using organoids to study radiation response, and discuss future directions for the applications of this technique.

Uncovering mutation-specific morphogenic phenotypes and paracrine-mediated vessel dysfunction in a biomimetic vascularized mammary duct platform

The mammary gland is a highly vascularized tissue capable of expansion and regression during development and disease. To enable mechanistic insight into the coordinated morphogenic crosstalk between the epithelium and vasculature, we introduce a 3D microfluidic platform that juxtaposes a human mammary duct in proximity to a perfused endothelial vessel. Both compartments recapitulate stable architectural features of native tissue and the ability to undergo distinct forms of branching morphogenesis. Modeling HER2/ERBB2 amplification or activating PIK3CA(H1047R) mutation each produces ductal changes observed in invasive progression, yet with striking morphogenic and behavioral differences. Interestingly, PI3Kα^H1047R ducts also elicit increased permeability and structural disorganization of the endothelium, and we identify the distinct secretion of IL-6 as the paracrine cause of PI3Kα^H1047R-associated vascular dysfunction. These results demonstrate the functionality of a model system that facilitates the dissection of 3D morphogenic behaviors and bidirectional signaling between mammary epithelium and endothelium during homeostasis and pathogenesis.

Loss of myoepithelial calponin-1 characterizes high-risk ductal carcinoma in situ cases, which are further stratified by T cell composition

A hallmark of ductal carcinoma in situ (DCIS) progression is a loss of the surrounding ductal myoepithelium. However, whether compromise in myoepithelial differentiation, rather than overt cellular loss, can be used to predict the risk of DCIS progression is unknown. Here we address this question utilizing pure and mixed DCIS cases (N = 30) as surrogates for DCIS at low and high risk for progression, respectively. We used multiplex immunohistochemical staining to evaluate the relationship between myoepithelial cell differentiation and lymphoid immune cell types associated with poor prognostic DCIS. Our results show that myoepithelial calponin-1 discriminates between pure and mixed DCIS lesions better than histological subtype, presence of necrosis, or nuclear grade. Additionally, focal loss of myoepithelial cells associated with increased PD-1+CD8+ T cells, which suggests a link between the myoepithelium and immune surveillance. To identify associations between calponin-1 expression and immune response, we performed unsupervised hierarchical clustering of myoepithelial and immune cell biomarkers on 219 DCIS lesions from 30 cases. Notably, the majority of pure (low-risk) DCIS lesions clustered in a high calponin-1, T cell low group, whereas the majority of mixed (high-risk) DCIS lesions clustered in a low calponin-1, T cell high group, specifically with CD8+ and PD-1+CD8+ T cells. However, a subset of pure DCIS lesions had a similar calponin-1 and immune signature as the majority of mixed DCIS lesions, which have low calponin-1 and T cell enrichment-raising the possibility that these pure DCIS lesions might be at a high risk for progression.

Organoid models for mammary gland dynamics and breast cancer

The mammary gland is a highly dynamic tissue that undergoes repeated cycles of growth and involution during pregnancy and menstruation. It is also the site from which breast cancers emerge. Organoids provide an in vitro model that preserves several of the cellular, structural, and microenvironmental features that dictate mammary gland function in vivo and have greatly advanced our understanding of glandular biology. Their tractability for genetic manipulation, live imaging, and high throughput screening have facilitated investigation into the mechanisms of glandular morphogenesis, structural maintenance, tumor progression, and invasion. Opportunities remain to enhance cellular and structural complexity of mammary organoid models, including incorporating additional cell types and hormone signaling.

Primary Mammary Organoid Model of Lactation and Involution

Mammary gland development occurs mainly after birth and is composed of three successive stages: puberty, pregnancy and lactation, and involution. These developmental stages are associated with major tissue remodeling, including extensive changes in mammary epithelium, as well as surrounding stroma. Three-dimensional (3D) mammary organoid culture has become an important tool in mammary gland biology and enabled invaluable discoveries on pubertal mammary branching morphogenesis and breast cancer. However, a suitable 3D organoid model recapitulating key aspects of lactation and involution has been missing. Here, we describe a robust and straightforward mouse mammary organoid system modeling lactation and involution-like process, which can be applied to study mechanisms of physiological mammary gland lactation and involution as well as pregnancy-associated breast cancer.

Development and characterization of mammary intraductal (MIND) spontaneous metastasis models for triple-negative breast cancer in syngeneic mice

Triple-negative breast cancer (TNBC) has a more aggressive phenotype and higher metastasis and recurrence rates than other breast cancer subtypes. TNBC currently lacks a transplantation model that is suitable for clinical simulations of the tumor microenvironment. Intraductal injection of tumor cells into the mammary duct could mimic the occurrence and development of breast cancer. Herein, we injected 4T1 cells into the mammary ducts of BALB/C mice to build a preclinical model of TNBC and optimized the related construction method to observe the occurrence and spontaneous metastasis of tumors. We compared the effects of different cell numbers on tumorigenesis rates, times to tumorigenesis, and metastases to determine the optimal number of cells for modelling. We demonstrated that 4T1-MIND model mice injected with 20,000 cells revealed a suitable tumor formation rate and time, thus indicating a potential treatment time window after distant metastasis. We also injected 20,000 cells directly into the breast fat pad or breast duct for parallel comparison. The results still showed that the 4T1-MIND model provides sufficient treatment time for lung metastases in mice and that it is a more reliable model for early tumor development. The 4T1-MIND model requires continuous improvement and optimization. A suitable and optimized model for translational research and studies on the microenvironment in TNBC should be developed.

Integrins as biomechanical sensors of the microenvironment

Integrins, and integrin-mediated adhesions, have long been recognized to provide the main molecular link attaching cells to the extracellular matrix (ECM) and to serve as bidirectional hubs transmitting signals between cells and their environment. Recent evidence has shown that their combined biochemical and mechanical properties also allow integrins to sense, respond to and interact with ECM of differing properties with exquisite specificity. Here, we review this work first by providing an overview of how integrin function is regulated from both a biochemical and a mechanical perspective, affecting integrin cell-surface availability, binding properties, activation or clustering. Then, we address how this biomechanical regulation allows integrins to respond to different ECM physicochemical properties and signals, such as rigidity, composition and spatial distribution. Finally, we discuss the importance of this sensing for major cell functions by taking cell migration and cancer as examples.

Cell interactions in collective cell migration

Collective cell migration is the coordinated movement of a physically connected group of cells and is a prominent driver of development and metastasis. Interactions between cells within migrating collectives, and between migrating cells and other cells in the environment, play key roles in stimulating motility, steering and sometimes promoting cell survival. Similarly, diverse heterotypic interactions and collective behaviors likely contribute to tumor metastasis. Here, we describe a sampling of cells that migrate collectively in vivo, including well-established and newer examples. We focus on the under-appreciated property that many - perhaps most - collectively migrating cells move as cooperating groups of distinct cell types.

Integrin α11β1 is expressed in breast cancer stroma and associates with aggressive tumor phenotypes

Cancer‐associated fibroblasts are essential modifiers of the tumor microenvironment. The collagen‐binding integrin α11β1 has been proposed to be upregulated in a pro‐tumorigenic subtype of cancer‐associated fibroblasts. Here, we analyzed the expression and clinical relevance of integrin α11β1 in a large breast cancer series using a novel antibody against the human integrin α11 chain. Several novel monoclonal antibodies against the integrin α11 subunit were tested for use on formalin‐fixed paraffin‐embedded tissues, and Ab 210F4B6A4 was eventually selected to investigate the immunohistochemical expression in 392 breast cancers using whole sections. mRNA data from METABRIC and co‐expression patterns of integrin α11 in relation to αSMA and cytokeratin‐14 were also investigated. Integrin α11 was expressed to varying degrees in spindle‐shaped cells in the stroma of 99% of invasive breast carcinomas. Integrin α11 co‐localized with αSMA in stromal cells, and with αSMA and cytokeratin‐14 in breast myoepithelium. High stromal integrin α11 expression (66% of cases) was associated with aggressive breast cancer features such as high histologic grade, increased tumor cell proliferation, ER negativity, HER2 positivity, and triple‐negative phenotype, but was not associated with breast cancer specific survival at protein or mRNA levels. In conclusion, high stromal integrin α11 expression was associated with aggressive breast cancer phenotypes.